Oklahoma scientists were really careful about announcing the connection between fracking activities and earthquakes

From the February 20, 2015 Science article, "Coping with earthquakes induced by fluid injection."
Science
Scientists are pretty sure that they know what is causing a wave of seismic activity in Oklahoma — but it has taken those actually employed by the state a while to come around.

Bloomberg reports that a representative from a major oil company told an Oklahoma scientist, Austin Holland, to "be careful when publicly discussing the possible connection between oil and gas operations and a big jump in the number of earthquakes" back in 2013.

Oklahoma recently surpassed California as the most seismically active state in the nation. Just five years ago, the state had barely any perceptible earthquakes on recent record. Scientists, including those at the US Geological Survey and in the journal Science, are now pretty sure that the increased seismic activity is due to oil companies injecting wastewater into the ground after using it during the hydraulic fracturing process.

According to Bloomberg, and previous reports from Energy Wire, which first reported on the pressure on Oklahoma scientists, the Oklahoma Geological Survey has been very slow to react to new evidence that the earthquakes might be tied to fracking's wastewater disposal.

Holland told both Energy Wire and Bloomberg that his hesitation to link the earthquakes and the wastewater injection is responsible scientific skepticism.

He told Energy Wire, "None of these conversations affect the science that we are working on producing. We have the academic freedoms necessary for university employees doing research."

The problem, of course, is that there's a pretty big conflict of interest for the state of Oklahoma, which employs Holland, and presumably a lot of pressure to be skeptical. The oil and gas industry — which use a lot of hydraulic fracturing these days — accounts for somewhere between 15 and 20% of all jobs in Oklahoma, based on the reports of Energy Wire and Bloomberg.

Here's a more concrete example of the Oklahoma scientists' skepticism, from Bloomberg:

Even when earthquakes appeared strongly correlated to wastewater injection, OGS has been reluctant to discuss a connection. In September 2013 a new disposal well was turned on in Love County in southern Oklahoma. Soon, quakes began to jolt the area, sometimes several a day.

The well reached its peak daily injection of more than 9,000 barrels of wastewater on Sept. 20, 2013. Three days later the area experienced a magnitude 3.4 quake, moving furniture inside homes and knocking down a chimney. Injection at the well was curtailed, then stopped altogether. The seismic activity dipped almost immediately.

Still, the OGS hesitated to link the two. "We cannot rule out that this observation could be simply a coincidence," Holland wrote in a report a week later. In early October, Holland spoke at a town hall meeting in Love County, where he again said no conclusions could be drawn about the cause of the quakes.

All of this said, Holland "recently told Bloomberg that the vast majority of the increase in earthquakes is due to the injection of oil and gas wastewater" and "bristles at any suggestion that industry pressure slowed him from reaching that conclusion."